Making Modern Carbide

Making Modern Carbide 

A precis of 

“Effect Of Metal and Cubic Carbide Additions on Interface Chemistry, Phase Composition and Grain Growth in WC-Co Based Cemented Carbides,”

By Jonathan Weidow

Department of Applied Physics,

Chalmers University of Technology

Gothenburg, Sweden, at +46 31-772

Carbide is made by combining various powders such as Tungsten, Carbon (Lamp Black), Cobalt and maybe Nickel, Chrome, Vanadium, Niobium, Titanium and Tantalum. 

Ideally these powders would be perfectly distributed and the industry is getting closer with finer, drier powders and better mixing and other manufacturing techniques.    

As these powders are sintered (using high pressure and a temperature below the melting point) the powders grow grains.  The powders natural tendency is to grow into large grains.  However smaller grains make much tougher, longer wearing carbidep_carbide.   The trick has been to make ever smaller grains and thus keep increasing carbidep_carbide performance.    

The hardness of cemented carbidep_carbides increases as the material’s grain size decreases and the number of grain boundaries correspondingly increases.  When used in metal cutting applications, the cemented carbidep_carbide tool substrate may deform plastically, and some of the boundaries between the tungsten-carbidep_carbide (WC) grains break and are infiltrated by a l0 nanometer to 50 nanometer binder layer.

Adding tiny portions of another substance (doping) the tungsten carbidep_carbide powder can dramatically limit grain growth. A 0.30 mass percent or 0.5 atom percent addition of Vanadium significantly limits grain growth.

The smallest grain size was for the material with the Vanadium additions.  Standard Tungsten Carbide had a grain size of 0.71 micron and a grain size distribution of 0.4 micron.  If you add a little Vanadium you get a grain size of 0.44 micron and a grain size distribution of 0.26 micron.  Therefore you get much smaller grains packed much closer together.  This greatly increases toughness, wear resistance, resistance to chemical attack and many other desirable properties.      

High-resolution electron microscopy was used to examine the materials atom by atom.  The vanadium formed a cubic structure between the tungsten carbidep_carbide grains and the Cobalt binder.  This structure was one to two atoms thick.  The Vanadium formed a layer or shield around the tungsten grains preventing them from growing larger by blocking off the exposure to more tungsten. 

The materials were analyzed by using an electrical field to evaporate atoms off individually.  As each atom was boiled off, it was weighed and identified by weight. 

Micrometer or Micron (um)

One millionth of a meter

0.000,039  (1/ 25,000 inch)

Nanometer (nm)

One billionth of a meter

0.000,000,039 inch (1/25,000,000 inch)

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